Nov 23, 2009

Science is Wrong: Yellow-breasted chat

Cornell Lab of Ornithology calls it "our largest wood-warbler." "Arguably our most distinctive wood-warbler" says David Sibley. Descriptions of the yellow-breasted chat inevitably mention its exceptional traits in the first breath. It's scientific name, Icteria virens, suggests it is an oriole, and ornithologists have hypothesized it may actually belong with tanagers, vireos or thrashers, yet it is considered a warbler.
I spent an afternoon in the library while in graduate school trying to learn why the chat is a warbler, and the only conclusion I could draw is that a respected scholar put it there decades ago, and no one has had the guts to overrule him. Sometimes science works that way, especially in biology with charismatic objects of study.
Phylogeny, the study of relationships among living things, is more of a historical discipline constrained by science than a pure science. Data is usually limited by extinctions or more mundane factors, and there is an art to choosing which sets of species to compare.
It is also important to choose the right traits. Variable traits like color and size can be deceptive, and usually you need more of a gestalt that may be hard to capture in numbers. Often researchers work with museum skins, pinned or voucher specimens, so the character of the living plant or animal can be obscure. I suspect the authority who called the chat a warbler was working mainly with dead specimens.
Live chats have a whole suite of behaviors that are uncharacteristic of warblers but fit right in with mimic thrushes. Their voice is quite similar to a catbird's, and like those and mockingbirds and thrashers, they do aerial dances above their nest. Such traits are less likely to be similar due to convergence than color. Many different kinds of birds migrate. Chats seem to have been classified as warblers because they are yellow and migrate. That's just wrong.
One of these days someone is going to use molecular data to prove that chats are mimic thrushes. That's one of my benchmarks for knowing when molecular phylogeny has matured from art and bullshit to real science.

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